Support getting token from path

Author: testower

lib/resty/pubsub/oauth_client.lua

@@ -28,6 +28,7 @@ function _M.new(self, oauth_config, topic)
 	local instance = {
 		topic = topic,
 		service_account_key_path = oauth_config.service_account_key_path,
+		service_account_token_path = oauth_config.service_account_token_path,
 		oauth_base_uri = oauth_config.oauth_base_uri,
 		oauth_scopes = oauth_config.oauth_scopes,
 		oauth_token_time = 0, -- We need to maintain token fetch time so that we can update it before expiring